The present invention relates generally to fastener screws, and more particularly to a novel fastener screw having improved installation characteristics which result in optimizing torque applied to the screw when securing a workpiece, such as a wooden plank, wood composite, or plastic, to a substrate, such as an underlying structural member, into which the screw is driven.
In many applications where fastener screws are employed to secure work pieces together, such as two or more pieces of wood or the like, it is desired that the screw be driven into the work pieces sufficiently so that the top of the screw head is flush with or recessed below the outer surface of the outermost workpiece. For example, in assembling wooden decks, it is a common practice to secure the deck planking to support joists or the like with flathead deck screws so that no part of the screw head protrudes above the upper deck surface.
In securing a workpiece, such as a deck plank, to a substrate, such as a joist, by deck screws as disclosed in U.S. Pat. No. 5,199,839, a threaded lead end of the screw is driven through the plank into the joist by applying rotational torque to the screw head. In deck screws of this type, an unthreaded shank or wire joins the screw head to the threaded lead end and normally extends at least partially through the plank when the threaded lead end is driven into the substrate or joist. In order to withstand the torque necessary to drive the threaded end through the plank into the substrate, the unthreaded screw shank or wire typically may have a diameter substantially equal to or greater than the major diameter of the screw thread. While sometimes necessary to provide sufficient strength, provision of a relatively large diameter shank appreciably increases the torque necessary to drive the screw through a workpiece and into the substrate because the periphery of the hole formed by the thread frictionally engages the shank and increases the resistance to rotation for a given size deck screw.
While not specifically drawn to deck screws, U.S. Pat. Nos. 471,179 and 470,804 to Jones disclose wood screws wherein a knurled surface is formed between the screw thread and a shank so that the knurled surface tends to enlarge the hole created by the screw thread as the screw is driven into a workpiece. The knurled surfaces on the screws are provided merely as an aid to thread rolling and are the same size as the shank. Thus, while the knurled surfaces slightly enlarge the holes created by the threaded ends of the screws, each shank continues to frictionally engage the perimeter of the hole created by the thread resulting in frictional drag between workpiece and shank.
U.S. Pat. No. 5,295,774 to Roberts discloses a screw which on first blush appears similar to the present invention. However, the Roberts screw is concerned with an entirely different problem than the present invention, namely, the protection of a screw shank coating in a corrosive environment in applications where a metal cladding must be secured to roof or wall structures. The Robert's screw protects the shank by reaming a hole in the metal cladding that may also be of the same diameter as the shank. If the Robert's screw were driven into a wooden workpiece, the hole created by the threaded end of the screw would not be enlarged by the knurled surface sufficiently to appreciably reduce the frictional drag between shank and workpiece.
Where the workpiece (i.e., deck planking) is relatively thick and has been treated or impregnated with a weather resistant material, the wood is generally tougher and more resistant to insertion of fastener screws. A fastener screw of the deck screw type which facilitates securing of wood members, such as deck planks, to wooden structural supports, and which is capable of reducing the frictional relation between the screw shank and deck plank would greatly reduce the torque necessary to overcome frictional resistance and significantly optimize the torque applied to drive the screw into the wooden support and countersink the screw head, thereby providing a substantial advance over prior deck screws.